Monocytes and macrophages secrete cytokines known as tumor necrosis factor alpha (TNFα) and tumor necrosis factor beta (TNFβ) in response to endotoxin or other stimuli. TNFα is a soluble homotrimer of 17 kD protein subunits (Smith et al., J. Biol. Chem. 262:6951-6954 (1987)). A membrane-bound 26 kD precursor form of TNF also exists (Kriegler et al., Cell 53:45-53 (1988)). For reviews of TNF, see Beutler et al., Nature 320:584 (1986); Old, Science 230:630 (1986); and Le et al., Lab. Invest. 56:234 (1987).
Cells other than monocytes or macrophages also produce TNFα. For example, human non-monocytic tumor cell lines produce tumor necrosis factor (TNF) (Rubin et al., J. Exp. Med. 164:1350 (1986); Spriggs et al., Proc. Natl. Acad. Sci. USA 84:6563 (1987)). CD4+ and CD8+ peripheral blood T lymphocytes and some cultured T and B cell lines (Cuturi et al., J. Exp. Med. 165:1581 (1987); Sung et al., J. Exp. Med. 168:1539 (1988); Turner et al. Eur. J. Immunol. 17:1807-1814 (1987)) also produce TNFα.
TNF causes pro-inflammatory actions which result in tissue injury, such as degradation of cartilage and bone, induction of adhesion molecules, inducing procoagulant activity on vascular endothelial cells (Fober et al., J. Immunol. 136:1680 (1986)), increasing the adherence of neutrophils and lymphocytes (Pober et al., J. Immunol. 138:3319 (1987)), and stimulating the release of platelet activating factor from macrophages, neutrophils and vascular endothelial cells (Camussi et al., J. Exp. Med. 166:1390 (1987)).
Recent evidence associates TNF with infections (Cerami et al., Immunol. Today 9:28 (1988)), immune disorders, neoplastic pathologies (Oliff et al., Cell 50:555 (1987)), autoimmune pathologies and graft-versus-host pathologies (Piguet et al., J. Exp. Med. 166:1280 (1987)). The association of TNF with cancer and infectious pathologies is often related to the host's catabolic state. Cancer patients suffer from weight loss, usually associated with anorexia.
The extensive wasting which is associated with cancer, and other diseases, is known as “cachexia” (Kern et al., J. Parent. Enter. Nutr. 12:286-298 (1988)). Cachexia includes progressive weight loss, anorexia, and persistent erosion of body mass in response to a malignant growth. The fundamental physiological derangement can relate to a decline in food intake relative to energy expenditure. The cachectic state causes most cancer morbidity and mortality. TNF can mediate cachexia in cancer, infectious pathology, and other catabolic states.
TNF also plays a central role in gram-negative sepsis and endotoxic shock (Michie et al., Br. J. Surg. 76:670-671 (1989); Debets et al., Second Vienna Shock Forum, p. 463-466 (1989); Simpson et al., Crit. Care Clin. 5:27-47 (1989)), including fever, malaise, anorexia, and cachexia. Endotoxin strongly activates monocyte/macrophage production and secretion of TNF and other cytokines (Kombluth et al., J. Immunol. 137:2585-2591 (1986)). TNF and other monocyte-derived cytokines mediate the metabolic and neurohormonal responses to endotoxin (Michie et al., New Engl. J. Med. 318:1481-1486 (1988)). Endotoxin administration to human volunteers produces acute illness with flu-like symptoms including fever, tachycardia, increased metabolic rate and stress hormone release (Revhaug et al., Arch. Surg. 123:162-170 (1988)). Circulating TNF increases in patients suffering from Gram-negative sepsis (Waage et al., Lancet 1:355-357 (1987); Hammerle et al., Second Vienna Shock Forum p. 715-718 (1989); Debets et al., Crit. Care Med. 17:489-497 (1989); Calandra et al., J. Infect. Dis. 161:982-987 (1990)).
Thus, TNFα has been implicated in inflammatory diseases, autoimmune diseases, viral, bacterial and parasitic infections, malignancies, and/or neurogenerative diseases and is a useful target for specific biological therapy in diseases, such as rheumatoid arthritis and Crohn's diseae. Beneficial effects in open-label trials with a chimeric monoclonal antibody to TNFα (cA2) have been reported with suppression of inflammation (Elliott et al., Arthritis Rheum. 36:1681-1690 (1993); Elliott et al., Lancet 344:1125-1127 (1994)). See also, Van Dullemen et al., Gastroenterology 109:129-135 (1995). Beneficial results in a randomized, double-blind, placebo-controlled trial with cA2 have also been reported with suppression of inflammation (Elliott et al., Lancet 344:1105-1110 (1994)).